a(n) = s(2n+1) - s(2n), where s( ) is sequence A023631.

Terms

a(0) =2a(1) =3a(2) =4a(3) =2a(4) =4a(5) =2a(6) =2a(7) =4a(8) =4a(9) =2a(10) =2a(11) =4a(12) =4a(13) =4a(14) =2a(15) =2a(16) =4a(17) =2a(18) =2a(19) =4a(20) =4a(21) =4a(22) =2a(23) =2a(24) =4a(25) =2a(26) =2a(27) =4a(28) =2a(29) =2